A wide variety of methods and apparatuses for detecting the surface topography of the cornea are known in which patterns are projected statically (e.g. DE 43 25 494 A1) or dynamically (e.g. DE 43 22 620 A1) onto the cornea and the pattern reflected or mirrored from the cornea is detected. Such methods are usually called video-keratometry, or ring projection according to Placido, and have proven their worth in general practice. They allow a point-by-point measurement of the corneal surface (mostly with more than eight thousand measuring points) within a few milliseconds.
The topography of the surface of the cornea is deduced from the position of the projection points and the relative relationship of these points that usually form a ring pattern. The reflected pattern is usually recorded by a charge-coupled device (CCD) array, with the CCD array (e.g., the CCD array of a video camera) usually being disposed coaxially and concentrically at the end of a so-called Placido's cone. This set-up leads to the consequence, however, that a central corneal region which has a diameter of approx. 0.5 mm cannot be detected during the measurement, although it is the central optical zone of the cornea that is particularly relevant to the determination of the refractive power of the eye and typically forms the pass-through point of the visual axis. The so-called Stiles-Crawford effect leads to the consequence that the central corneal zone which is free from any patterns during the projection of Placido's patterns plays a special role with respect to the peripheral corneal regions in the eye's projection system.
Moreover, video-keratometry, which occasionally is also designated as video-topography, is unable to supply any information on the back surface of the cornea and the lower sections of the refractive system of the eye, in particular the front side and back side of the lens. The geometry of the boundary surface, the depth of the anterior chamber of the eye, the boundary surface properties and the topography of the lens, the distribution of density and the scattering body arrangements in the lens and the depth of the posterior chamber of the eye (as defined by the distance between lens and retina) are the prerequisites for increasing the precision of refractive measures on the cornea and for implantation-surgical interventions on the lens for the computer-aided detection and analysis of the refractive system of the optical properties of the entire eye in a patient.
Keeping this in mind, one object of the present invention is to provide a method and an apparatus that allow detecting in a simple and rapid manner both the entire substantial surface topography of the cornea and also at least one optical property of the layers of the eye disposed under the cornea.